November 4, 2015
Anaphylaxis Is Extremely Rare Side Effect of Flu Vaccine

Atlanta—The risk of severe adverse reaction worries for every pharmacist who administers influenza vaccine.

A new study finds, however, that anaphylaxis, among the worst of the adverse reactions, is extremely rare. The report in the Journal of Allergy and Clinical Immunology notes that little information has been available on the risk of the potentially life-threatening allergic reaction in adults or with newer vaccines in children.

An investigative team led by researchers from the Immunization Safety Office of the CDC sought to remedy that, estimating the incidence of anaphylaxis after vaccines, as well as describing the demographic and clinical characteristics of the condition.

For the study, the researchers used data from the Vaccine Safety Datalink, first identifying all patients with a vaccination record from January 2009 through December 2011 and then using diagnostic and procedure codes to identify potential anaphylaxis cases.

After reviewing the medical records of potential cases, the study team determined which of the anaphylaxis cases met the Brighton Collaboration definition and had been triggered by vaccination. The incidence of anaphylaxis after all influenza vaccines combined was calculated as well as for selected individual vaccines.

Overall, the study identified 33 confirmed vaccine-triggered anaphylaxis cases that occurred after 25,173,965 vaccine doses, making the rate of anaphylaxis 1.31 per million vaccine doses.

Results indicate that incidence did not vary significantly by age although a nonsignificant female predominance was determined.

Vaccine-specific rates included1.35 per million doses for inactivated trivalent influenza vaccine (10 cases among 7,434,628 doses given alone) and 1.83 per million doses for inactivated monovalent influenza vaccine (2 cases among 1,090,279 doses given alone).

Symptom onset occurred within 30 minutes in eight cases, in 30 to less than 120 minutes in another eight cases, two to less than 4 hours in 10 cases, 4 to 8 hours in two cases and the next day in one case. The time to severe allergic reaction was not documented in four cases.

“Anaphylaxis after vaccination is rare in all age groups,” study authors conclude. “Despite its rarity, anaphylaxis is a potentially life-threatening medical emergency that vaccine providers need to be prepared to treat.”

More common side effects for the inactivated influenza vaccine, the cell culture–based inactivated influenza vaccine and recombinant influenza vaccine are pain, redness, and swelling at the injection site, according to the CDC. Fever, malaise, and myalgias are usually mild and go away on their own, public health officials add.

Live, attenuated influenza vaccine, administered as an intranasal vaccine, is more likely to cause rhinitis and nasal congestion than the other vaccines in both adults and children, the CDC points out.
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